Computer systems are often connected to a communication network via telephone lines. A popular means for connecting computer systems to a network is over a digital subscribed line (DSL). DSLs come in many varieties including asymmetric (ADSL), symmetric (SDSL), rate-adaptive (RADSL), and very high bit-rate (VDSL).
The DSL shares the same physical wire as a common telephone line. The telephone wire is a twisted pair of copper wires, which has a maximum signal bandwidth from 300 kHz-10 MHz., depending on the length of the line. Since a typical voice communication requires only a portion of the total bandwidth (e.g., around 4 kHz) available on the telephone line, the additional unused bandwidth is available on the line for the DSL communication without interfering with telephone communication.
A subscriber device such as a computer communicates with a service provider via a DSL modem. The DSL modem is physically connected between the subscriber device and the telephone wire, and includes a DSL line driver. The DSL line driver includes a power amplifier that delivers a signal to the telephone line.